Enhanced photochemistry on silver surfaces

Pyrazine and triazine are found to photofragment on rough silver surfaces to form graphitic carbon as a major product. The rate‐determining step is found to be biphotonic. The enhanced photochemistry is shown to take place most efficiently directly at the metal surface rather than a short distance above the surface as would be expected on the basis of a competition between nonradiative relaxation of the excited molecule and excitation by the surface‐enhanced electric field. Moreover, it was found possible to increase the photolysis rate further by overcoating the adsorbed molecules with an appropriate number of layers either of the photoreagent itself or of another molecule, tuning thereby the localized surface plasmon of the rough surface into resonance with the exciting laser. We suggest that in a previous report [Goncher, Parsons, and Harris, J. Phys. Chem. 88, 4200 (1984)] of enhanced photochemistry at rough surfaces the effect of displacing the photoreagent from the surface using spacer layers was in...

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